Polymeric ultrafiltration membranes are commonly prepared by the phase inversion method (R. E. Kesting, 1971, Synthetic Polymeric Membranes, McGraw-Hill) in which a thin film of a polymer solution is solidified by immersion in a bath containing a nonsolvent. Poly(acrylonitrile) can be dissolved in polar organic solvents such as Dimethyl formamide (DMF), dimethyl acetaraide (DMAc), or dimethyl sulfoxide (DMSO) for purposes of membrane preparation (U.S. Pat. No. 4,025,439). By virtue of relatively low cost, solvent power and safety in handling, dimethyl formamide is a preferred solvent for preparing the polyacrylonitrile containing solution. For similar reasons, water is a preferred non-solvent.
The use of copolymers based on acrylonitrile with other monomers has been suggested as materials for ultrafiltration membranes e.g. U.S. Pat. No. 4,181,694 (isobutane, vinyledene chloride, butadiene, methacrylonitrile, ethylene vinyl ether as comonomers), U.S. Pat. No. 3,950,2579 vinyl pyrrolidone as comonomer) and U.K patent application GB 2,096,941 A (methyl metacrylate and sodium salt of vinylsulfonic acid as comonomers).
The prior art mentioned above does not describe the preparation of PAN (polyacrylonitrile) membranes using carboxylic acids. The Applicants (previous) Indian Patent (1811/DEL/96) has mentioned the preparation of membranes made of Polyacrylonitrile and its copolymers for purification of water. The objective of this invention remains the same, namely, aiming of a very high water permeating ability for better commercial usage of the membranes made thereof and keeping the separation properties the sane.